If you set the DHCP servers at a subnet level, an subsequent ranges you create in the subnet will allow you to just inherit the associated OPH. However, any existing ranges in the subnet will not allow any “use subnet OPH” option. For any existing ranges in the subnet, you will need to recreate them if you want them to inherit the subnets OPH assignment values.

For Advanced Active/Passive DHCP the lease DB is manged differently so it can be shared. It is shared via BloxOne CSP so the two DHCP servers don't have to talk to each other (although they do for heartbeats). Only ever do Kia Active/Passive if both devices are in the same VLAN. Because active has to stream updates immediately to passive (not Lazy Update). MS Delay between devices - Multiply by four and then how many of those you can fit into a second. That is how many LPS you can service in Active/Passive HA.

Because in Active/Passive the two nodes of NIOS-X need to sync with each other before issuing a lease, the latency between the two devices has a massive impact on how many leases the devices can issue per second.

(1000ms / latency_between_peers) = LPS

• 500ms = 2 LPS
• 125ms = 8 LPS
• 100ms = 10 LPS
• 50ms = 20 LPS
• 25ms = 40 LPS

• Advanced Active/Passive - Use this. It is good.
• Active/Passive - This is okay but Advanced Active/Passive is preferable due to the specifics of how the redundancy works. A/P should be co-deployed while AA/P can be hub-and-spoke or multi-site.
• Active/Active - Has limited value in BloxOne. Never use it. If it is used, both units should only be deployed at the same site and the DHCP scopes must be at least 200% in size for what’s needed. If you have 100 DHCP clients, your scope must be a minimum of 200 IP addresses.
• Anycast - Don't use unless you really know what you are doing and you have a very specific use case for it.

If you have active/passive and both servers are running but the communication link between them fails, DHCP “should” still function. Both servers will see the packets from the client, even if they can't talk to each other. They will know if the other is providing addresses. That said, there's likely to be conflicts BUT the client should do a RARP if the address is in use because one of the servers successfully issued a license.